Since azakai is too humble to mention his own qualifications, I want to point out that is the author of the Emscripten LLVM-to-JS compiler, and the BananaBread

Since azakai is too humble to mention his own qualifications, I want to point out that is the author of the Emscripten LLVM-to-JS compiler, and the BananaBread first-person-shooter demo linked above, so when he talks about the limits of JS performance compared to C, he really knows what he's talking about. :)